1. Field of the Invention
Embodiments of the present disclosure relate to microemulsion flowback recovery compositions for use in oil and gas production and methods for making and using same.
More specifically, embodiments of this disclosure relate to microemulsion flowback recovery compositions of water recovery during well stimulation or hydraulic fracturing, where the compositions include non-flammable, non-combustible, non-hazardous, and/or environmentally friendly organic solvent systems.
2. Description of the Related Art
Recovery of injected water has become increasingly important, as the presence of water particularly in the near-wellbore area is detrimental to the production of oil and gas. Drilling and stimulation fluids can increase the connate water saturation of the formation, as can mud drilling fluids by mud filtrates and filter cakes being pushed into pore spaced in the formation blocking pathways for water recovery and oil and/or gas production.
The difficulty in moving fluids that are trapped in the pore spaces of the rock is due largely to capillary pressure. Capillary pressure is the pressure difference across the interface between two immiscible fluids. According to Young-Laplace equation, the capillary pressure (pc) is directly proportional to the interfacial tension (γ) between two immiscible fluids, and inversely proportional to the radius of the interface (r), given by the following equation.
      p    c    =            2      ⁢      γ      ⁢                          ⁢      cos      ⁢                          ⁢      θ        r  
The high interfacial tension between oil and water, coupled with a small pore throat radius, results in a high capillary pressure in many oil and gas bearing formations. Surfactants have been used to decrease interfacial tension between oil and water. A reduction in interfacial tension between an injected fluid and hydrocarbons has been achieved using microemulsions. A microemulsion is a thermodynamically stable mixture of oil, water, surfactants, and sometimes solvents and co-solvents. These solvents and co-solvents are commonly referred to as coupling agents. Oil-water-surfactant blends that are used to remove water trapped in the pores of a hydrocarbon-bearing formation are typically referred to as flow-back or water recovery additives. When these water recovery additives are added to a stimulation fluid, the interfacial tension between the aqueous stimulation fluid and the hydrocarbons in the well is reduced by orders of magnitude. The resultant reduction in capillary pressure allows penetration of the stimulation fluid into the pore spaces of the rock, where it can co-mingle with the connate water. During production, the injected fluid is removed, thus opening up pathways for hydrocarbons.
Water recovery additives frequently contain flammable chemicals, such as terpenes and short chain primary alcohols, because they are effective solvents or coupling agents. One example of a coupling agent is isopropanol, which is used to stabilize many different combinations of oil and surfactant. Terpenes, such as d-limonene, are commonly used as the oil phase in water recovery microemulsions.
The flammability of these solvents makes them hazardous to handle. For instance, d-limonene has a flash point under 140° F. and is a regulated material under the U.S. Department of Transportation. In addition, d-limonene is an aquatic hazard and carries the “dead fish” placard in transit. In light of these drawbacks in known water recovery compositions, there is still a need in the art for compositions that are capable of reducing interfacial tension to levels conducive for water recovery, while avoiding the handling and transportation issues associated with flammable solvents.